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Dissolved Methane in the Sills Region of the Gulf of California
Citation:
Macias-Zamora, J., K. Castro-Morales, R. Burke, AND M. Lopez-Mariscal. Dissolved Methane in the Sills Region of the Gulf of California. Ciencias Marinas . Universidad Autónoma de Baja California, Ensenada, B.C., Mexico, 39(2):119-135, (2013).
Impact/Purpose:
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Description:
An unusual combination of features make the midriff islands region of the northern Gulf of California (NGC) a strong source of methane to the atmosphere. Oceanographic isolation from the rest of the NGC by a series of sills and islands along with enhanced upward transport of nutrient-rich water masses by tidal currents, upwelling, and overflows result in high productivity. One potential consequence of the high productivity is the generation of elevated dissolved methane concentrations and methane super-saturation. We found elevated methane concentrations throughout our study area, the highest of which occurred inside the Ballenas Channel (BC), which was super-saturated at all depths. A lower level of methane super-saturation was measures south of the sills area, where a well-defined oxygen minimum zone was previously reported. Data from 22 stations in the NGC suggest southward advection of methane via the methane-rich Gulf of California Water (GCW) mass. The vertical methane distribution shows that highly elevated dissolved methane concentrations are mainly associate with GCW and, to a lesser extent, subsurface subtropical water. Our observations of super-saturated methane concentrations at all stations and all depths in the BC suggest that the BC is a strong source of methane to the atmosphere. In particular, station 7 at 50, 20 and 10 m depths had methane concentrations of 49.1, 48.3 and 43.5 nM respectively, which correspond to saturation values of 2090, 2050 and 1850%, respectively. Methane fluxes calculated from BC surface water methane concentrations ranged from 3.4 to 103.4 µmol Ch4 M-2 d-1. These values are higher than those measures at many other high productivity sites worldwide including upwelling sites. The average methane flux calculated for our entire study area was 21.1 µmol CH4M-2d-1.
